The proposed research addresses issues in executive control of cognitive processing that are central in basic research in cognitive science, cognitive neuroscience, lifespan development, and individual differences. These issues have direct implications for mental health. Deficits in executive control have been identified in several disorders, including schizophrenia and attention deficit hyperactivity disorder. The main goal of the research is to develop behavioral methods for distinguishing between top-down effects that truly reflect executive control and bottom-up effects that mimic it. This issue is important in designing and interpreting measures of executive control in other areas of research, especially research on deficits in mental disorders. The goal of distinguishing top-down from bottom-up effects will be accomplished by developing and evaluating a priming model that attempts to account for behavior in task-switching experiments purely in terms of bottom-up processes. The footprints of executive control may be seen in the situations in which the priming model fails to provide a complete account. According to the priming model, top-down control may be required for peripheral processes but not for central processes. Perceptual and motor processes and orienting of attention may require executive processing, but memory retrieval does not. This hypothesis leads to two specific aims: (1) To develop the priming model and test its fundamental assumptions in experiments that require switching between central tasks that can be performed by memory retrieval. (2) To push the limits of the priming model by testing it in experiments that require switching perceptual and motor systems and changing the orientation of attention. The first aim will establish the validity of the model, the second will establish its limits and set the stage for a general model of executive control.